Positive electrode active material for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery

Abstract

Provided is a positive electrode active material which contributes to improvement of charge/discharge cycle characteristics of a nonaqueous electrolyte secondary battery. This positive electrode active material contained in the nonaqueous electrolyte secondary battery has a layered structure and contains a lithium transition metal composite oxide having a predetermined composition. The lithium transition metal composite oxide contains secondary particles formed from aggregates of primary particles, wherein: a first surface decorative layer, which contains a Ca element and/or an Sr element and at least one kind of element selected from the group consisting of W, Mo, Ti, Si, Nb, and Zr, is present on the surface of the primary particles; and a second surface decorative layer, which contains at least one kind of element selected from the group consisting of Al, Zr, B, W, Ti, Mg, Co, and Si, is present on the surface of the secondary particles.

1 . A positive electrode active material for non-aqueous electrolyte secondary battery, including
 a lithium transition metal composite oxide which has a layered structure and which is represented by general formula Li x Ni a Co b Mn c M1 d O 2-y  (where 0.95≤x≤1.05, 0.75≤a≤0.95, 0≤b≤0.15, 0≤c≤0.25, 0≤d≤0.10, 0≤y<0.05, a+b+c+d=1, and M1 is at least one element selected from the group consisting of W, Mg, Mo, Nb, Ti, Si, Al, and Zr), wherein   the lithium transition metal composite oxide includes secondary particles formed by aggregation of primary particles,   a first surface modification layer containing at least one of Ca and Sr and also containing at least one element selected from the group consisting of W, Mo, Ti, Si, Nb, and Zr is present at a surface of the primary particles, and   a second surface modification layer containing at least one element selected from the group consisting of Al, Zr, B, W, Ti, Mg, Co, and Si is present at a surface of the secondary particles.   
     
     
         2 . The positive electrode active material for non-aqueous electrolyte secondary battery according to  claim 1 , wherein a total amount of Ca and Sr contained in the first surface modification layer is less than or equal to 3 mol % based on a total number of moles of metal elements other than Li in the lithium transition metal composite oxide. 
     
     
         3 . The positive electrode active material for non-aqueous electrolyte secondary battery according to  claim 1 , wherein a total amount of W, Mo, Ti, Si, Nb, and Zr contained in the first surface modification layer is less than or equal to 2 mol % based on a total number of moles of metal elements other than Li in the lithium transition metal composite oxide. 
     
     
         4 . The positive electrode active material for non-aqueous electrolyte secondary battery according to  claim 1 , wherein a total amount of Al, Zr, B, W, Ti, Mg, Co, and Si contained in the second surface modification layer is less than or equal to 2 mol % based on a total number of moles of metal elements other than Li in the lithium transition metal composite oxide. 
     
     
         5 . The positive electrode active material for non-aqueous electrolyte secondary battery according to  claim 1 , wherein a compound represented by general formula M2 α M3 β O γ  (where 1≤α≤2, 1≤β≤5, 4≤γ≤9, M2 is at least one element selected from Ca and Sr, and M3 is at least one element selected from the group consisting of W, Mo, Ti, Si, Nb, and Zr) is adhered to the surface of the primary particles of the lithium transition metal composite oxide. 
     
     
         6 . A non-aqueous electrolyte secondary battery, comprising a positive electrode including the positive electrode active material for non-aqueous electrolyte secondary battery according to  claim 1 , a negative electrode, and a non-aqueous electrolyte.